This invention relates to compression hubs of the type that are employable in cooperative association with a plurality of magnets in a fusion reactor system, and, more particularly, to such a compression hub which is equipped with eddy current prevent means operable to impede the circulation therethrough of eddy currents induced by changes in the magnetic flux field.
One form of fusion reactor that has been proposed for use by the prior art is the so-called Tokamak-type reactor. In accordance with the mode of operation of this type of reactor, thermal power is generated as a consequence of the ignition of plasma. There exists, however, in this type of reactor not only a need to ignite the plasma, but also a need for effecting control over the plasma.
One technique which has been proposed for use for purposes of effecting control over the plasma is that of magnetic confinement. More specifically, it has been proposed to employ for this purpose a plurality of superconducting magnets operating at cryogenic temperatures. Through the use of such magnets, it is possible to attain intense magnetic fields of a strength sufficient to effect the desired confinement of the plasma.
To produce the desired result, the superconducting magnets are preferably arranged relative to each other so that they extend outwardly from a common point, in a manner similar to that of the spokes of a wheel. These magnets generate intense forces, tending to draw them together to the common point. Thus, there is a need created to provide means operative to resist the forces tending to draw the magnets together. One means contemplated for use for this purpose is a compression hub, also commonly referred to as a bucking post.
One form of a compression hub, which is suitable for use for the afore-described purpose, comprises the subject matter of my earlier U.S. Pat. No. 4,174,254, which issued on Nov. 13, 1979, and which is assigned to the same assignee as the present invention. As discussed therein, a compression hub, in order to be suitable for use for the purpose described above, must be susceptible to being cooled to the same relative temperature as the superconducting magnets, i.e., to cryogenic temperatures. In addition, this cooling of the compression hub must be capable of being accomplished while at the same time ensuring that the structural adequacy of the compression hub is maintained.
Regarding the matter of cooling, as set forth in my aforementioned earlier issued U.S. patent, the normal operative temperature range for the superconducting magnets is 4.2.degree. to 4.9.degree. kelvin. To achieve this range of temperatures, the magnets are preferably cooled by liquid helium, which boils at 4.2.degree. kelvin at atmospheric pressure. Because of the criticality of the operating temperature, it is necessary that the compression hub, which is cooperatively associated with the superconducting magnets, be cooled also to the same temperature as the magnets. Otherwise, heat transfer in the form of a heat loss could take place between the compression hub and the magnets cooperatively associated therewith whereby the operating effectiveness of the magnets would be seriously impaired.
Not only is it necessary that the operating temperature of the compression hub be maintained at the same operating temperature as the superconducting magnets, but also it is important that the compression hub be capable of being cooled to the desired operating temperature of 4.2.degree. kelvin in a relatively short period of time. One method of effecting the desired cooling of the compression hub is to depend on the cooling effect of the magnets to remove heat from the compression hub. However, this could take an inordinate amount of time to achieve, which would be totally unacceptable from the standpoint of how long it takes to render the system operative, particularly in a start-up situation. The reason for this, as discussed in my aforementioned earlier issued U.S. patent, is that at these very low temperatures the thermal gradient between the compression hub and the magnets cooperatively associated therewith is so small that virtually no cooling of the compression hub is effected. It, therefore, becomes necessary to supply coolant to the compression hub itself. More specifically, fluid flow paths must be established for coolant in the compresion hub. However, as noted previously hereinabove, the coolant flow paths in the compression hub must be provided in such a manner as to not adversely affect the structural adequacy of the compression hub, i.e., the ability of the compression hub to resist the forces tending to draw the magnets together to a common point.
One form of compression hub, which fulfills the above-stated requirements for a compression hub employable in a Tokamak-type fusion reactor system, has been described and illustrated in my aforementioned earlier issued U.S. patent. In addition, an alternative form of construction for a compression hub, which also satisfies the above-stated requirements, comprises the subject matter of Penfield patent application, Ser. No. 000,047, filed on Jan. 2, 1979, which issued on Sept. 1, 1981 as U.S. Pat. No. 4,287,022, and assigned to the same assignee as the present invention. To summarize, these two alternative forms of construction for a compression hub are deemed to be equally suitable for use in a Tokamak-type fusion reactor system insofar as concerns fulfilling those requirements for such a structure, which have been stated hereinbefore.
However, in addition to those requirements that have been set forth above, it is also desirable that a compression hub embody means operable for impeding the circulation therethrough of eddy currents. The latter, as is known to those skilled in the art, comprise those currents which are induced in the body of a conducting mass as a consequence of a variation in magnetic flux. The presence of circulating eddy currents would disadvantageously characterize the compression hub, insofar as concerns the ability of the latter to provide the type of performance being sought therefrom, when the latter is being employed in cooperative association with a plurality of superconducting magnets in a Tokamak-type fusion reactor system. Accordingly, it is contemplated in accord with the present invention to interrupt the surface of the elements that collectively comprise the compression hub so as to prohibit the circulation through the latter of the aforedescribed eddy currents. However, there is a need to accomplish the aforesaid interruption in the surfaces of the elements without adversely affecting either the strength of the compression hub, i.e., the capability of the latter to successfully resist the forces tending to draw the magnets thereagainst, or the ability of the compression hub to be cooled to a satisfactory level, i.e., the existence of a sufficient flow of coolant through the compression hub so as to enable the latter to be cooled to a temperature of 4.2.degree. kelvin. In summary, there has been deemed to exist a need to provide a compression hub with suitable means to insure that the latter will not be disadvantageously characterized as a result of the inducement therein of eddy currents that would otherwise be free to circulate therethrough.
It is, therefore, an object of the present invention to provide a compression hub that is designed to be cooperatively associated with a plurality of superconducting magnets in a Tokamak-type fusion reactor system.
It is another object of the present invention to provide such a compression hub which embodies sufficient structural strength as to be capable of resisting the intense forces produced by the superconducting magnets that tend to draw the latter together towards a common point whereat the compression hub is located.
It is still another object of the present invention to provide such a compression hub which embodies a construction that permits the latter to be cooled to a temperature that is commensurate with the operating temperature of the superconducting magnets, while yet enabling the compression hub to retain the structural strength required thereof.
A further object of the present invention is to provide such a compression hub which embodies means operative to impede the circulation of eddy currents therethrough, while yet possessing the strength and cooling characteristics desired therefrom.
A still further object of the present invention is to provide a compression hub embodying such eddy current prevent means wherein the latter consists of an interruption provided in the surface of the elements that collectively comprise the compression hub.
Yet another object of the present invention is to provide such a compression hub embodying eddy current prevent means wherein the interruption provided in the surface of the elements takes the form of a radial cut in which an insulative material is inserted.
Yet still another object of the present invention is to provide a compression hub embodying eddy current means wherein the interruption provided in the surface of the elements is effected by fabricating the elements from multiple segments that in the assembled state are separated one from another by means of insulative material.